Microwave generator having pulsed ferrite body



H.J. SHAW ETAL 3,368,162

MICROWAVE GENERATOR HAVING PULSED FERRITE BODY Feb; 6, 1968 2 Sheets-Sheet 1 Filed May 17, 1966 5W m i N mam/WWW w W m 4 EH r AW Mm M W H. J. SHAW ETAL MICROWAVE GENERATOR HAVING PULSED FERRITE BODY Feb. 6, 1968 2 Sheets-Sheet 2 Filed May 1 7, 1966 SGURCJE OF DEN/1N6 CURRENT INVENTORS J. SHAW KARP AWO/QNEYS @57 5 BY Y L? CALM United States Patent Office 3,368,162 MICROWAVE GENERATOR HAVING PULSED FERRITE BODY Herbert J. Shaw, Stanford, and Arthur Karp, Los Altos,

Calif assignors to Research Corporation, New York,

N.Y., a non-profit corporation of New York Filed May 17, 1966, Ser. No. 550,858 11 Claims. (ill. 331-96) This invention relates to apparatus for generating and etficiently propagating microwaves in waveguides and the like, and more particularly to improvements therein.

The increased use of progressively higher microwave frequencies in modern communication, radar and other applications has increased the demand for microwave generators having increased power capabilities, which still retain simplicity, high efficiency and small size. One method used for the generation of coherent microwaves employs ferrite material as a resonator, subjecting it to a suitable pulsed magnetic field which results in the generation of microwaves. Devices using ferrites have been constructed which used a pulsed magnetic field to translate upward the frequency of an essentially continuous wave input signal. However, these devices have low efiiciency and are inherently limited to low power levels. No suitable method has heretofore been found for utilizing pulsed magnetic fields to obtain efiicient, high power microwave generators, particularly at the higher microwave frequencies.

Accordingly, one object of the present invention is to provide a more efficient, high microwave power generating apparatus than has been available heretofore.

Another object of this invention is to provide a microwave generator having a simple construction, yet providing a high output power.

Still another object of this invention is to provide a compact and reliable means for generating microwaves of high power using pulsed currents, and for coupling these microwaves to Waveguides and the like.

The foregoing and other objects are realized by a microwave generator which utilizes a body made of ferrite material as a resonator. The ferrite body is placed between the poles of a permanent magnet. Pulsed 'currents of very short rise times are circulated in a novel coil structure placed about the ferrite to create a magnetic field having a rapid increase in intensity. The rapidly changing field together with the field of the permanent magnet causes magnetization in the ferrite body to oscillate at microwave frequencies. In order to couple the microwave energy of the ferrite element to a waveguide structure, effectively a resonant chamber is provided adjacent to the ferrite. The chamber is obtained by splitting the coil structure which is disposed about the ferrite, into two coil halves, electrically connected in parallel. The space between the coil halves serves as a resonant microwave coupling element between the resonator and waveguide structure. By utilizing such apparatus, x-band microwaves of the energy of several hundred watt nanoseconds have been generated in pulses of about one to two nanoseconds seconds) duration each.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is an exploded view of a waveguide coupling device constructed in accordance with the invention;

FIGURE 2 is a sectional front elevation View of the coupling device of FIGURE 1; and

3,368,162 Patented Feb. 6, 1968 FIGURE 3 is a perspective view of the coil and slot resonator structure of the invention.

Apparatus in accordance with this invention is shown in exploded form in FIGURE 1 and may comprise a waveguide 10 in which microwaves are to be propagated. A housing 11 for holding microwave generating and propagating apparatus is positioned between two flanges 12 and 14, and two dielectric insulators 16, 17, such as Lucite. A coupling control means, comprising a short length of waveguide, 18, within which is placed a movable shorting element 20, serves to control the coupling to the waveguide of waves which are generated. A magnet 22 has two poles (only one of which is shown), which are respectively placed on opposite sides of the housing 11, to create a uniform magnetic field through the area occupied by the housing.

A more detailed and enlarged view of the microwave generating and coupling apparatus in accordance with this invention is shown in FIGURE 2. A novel coil structure 24 is mounted on the housing 11 in a manner to be disposed within a waveguide aperture 25. The coil structure is connected to two strip line conductors 26. The conductors 26 carry current to the coil 24 which can then create an intense magnetic field in the space within the coil, which is in addition to the field established by the permanent magnet 22. A dielectric probe 28 carries a ferrite element 30, the element generally being located at the center of the coil 24. A resonator tuning screw 32 carries a capacitive disc 34 (such as made of rutile) which serves to tune a resonant slot 42 (shown in FIGURE 3) to cause the generation of microwaves having a desired frequency within a particular range. Waveguide tuning screws 36 alter the susceptance of the coil to more effectively couple microwaves to the waveguide.

The generation and propagation of microwaves occur when a large pulse of current is sent through the conductors 26. The current flowing through the coil 24 creates a magnetic field in the region occupied by the ferrite element 30. When the field created by the coil 24 and the permanent magnet 22 has a sufficiently high initial time rate of rise, the element oscillates and generates micro- Waves. Before microwaves of high energy can be propa: gated through the waveguide 10, however, a means must be provided for coupling the ferrite-generated microwaves to the waveguide. This function is performed by a resonator slot 42 formed in the coil 24.

The coil 24, which is shown in detail in FIGURE 3, comprises a Wide single loop structure forming a central aperture 40. A transverse slot 42, which is the resonator slot, is formed at the mid-point of the longitudinal axis of the loop structure, separating it into two halves 44 and 46. Each half 44 or 46 is a coil, disposed coaxially with the other coil and separated a predetermined distance d thereform. The coil halves are electrically connected in parallel to a source of driving current 27 (see FIGURE 2). Mounting nuts, 52, attached to the coil, serve to provide a means whereby the coil is supported within the housing by screws 53 (see FIGURE 2).

In order to generate microwaves in the ferrite element, currents of very rapid rise times must be conducted through the coil 24. The magnetic field of the coil, while perpendicular to that of permanent magnet 22 (in the region occupied by the ferrite element 30), adds to it vectorially, resulting in a field that rotates as the coil current increases. As the coil current increases on the leading edge of the current pulse, the frequency of oscillation of the ferrite element 30 increases. When the oscillation frequency reaches the resonant frequency of the slot resonator 42 formed by the space between the coil halves, the slot resonator draws energy from the ferrite element, and the resonator then continues to oscillate 33 21 its own resonant frequency, and this oscillation is damped by the coupled waveguide.

The lowest normal mode of the slot resonator 42 has a radio frequency magnetic field which. extends through the space between the coil halves. The slot radio fre quency magnetic field is thus oriented transversely to the waveguide axis and is coaxial with the transverse radio frequency magnetic field of the waveguide normal mode. Accordingly, the slot resonator 42 is tightly coupled to the TE waveguide mode, and efficiently transfers energy from the ferrite element to the waveguide. It may be noted that the normal mode field of the slot resonator 42 is not coupled back to the coil 24 because of the coil symmetry, and therefore energy in the slot is available for transfer in the waveguide mode.

The radio frequency magnetic field of the lowest normal mode of the slot also extends through the interior of the pulses field coil and thus, in particular, through the region occupied by the ferrite sample. This slot mode field is very strong at the location of the sample, and thus also provided very tight radio frequency coupling between the slot resonator and the ferrite sample.

The housing 11 extends less than 260 to form a hiatus or slit 55 through which he coil 24 is inserted. The coil 24 is typically mounted with each end 55 and 57 in contact with opposite walls of the housing so that there is only one longitudinal gap through which radio frequency leakage might occur. A portion of the current pulse delivered by the conductors 26 flow through the housing 11 by following a path around the waveguide aperture 25. However, the relatively high inductance of theouter path results in only a small loss in field strength at the element 30. The dielectric insulators 16, 17 prevent pulse current flow through the waveguides 10, 18.

The frequency of oscillation can be varied over a wide range by turning the screw 32 to move the rutile disc 34 toward or away from the mouth of the slot. While the disc 34 varies the frequency, the loaded Q of the slot circuit can be varied by moving the shunting element 20.

The divided loop arrangement of the coil, by concentrating the transverse magnetic field in the manner described, turns the loop into an asset rather than the liability which it would ordinarily be, by reason of its obstruction and shielding of the ferrite element from the waveguide fields.

Microwave generators of the type described above have been constructed and tested. By way of example and not by way of a limitation, an x-band apparatus has been constructed utilizing a coil having a width S of & inch, a length l of 0.142 inch, 21 slot width d of 0.032 inch, a hole diameter of inch, and a separation p between conductors of 0.026 inch. This resulted in a structure with an inductance of approximately one nanohenry capable of producting a magnetic field on the order of 2,700 oersteds per kiloampere.

The coil was mounted in a housing forming a waveguide with internal dimensions of 0.4 inch by 0.9 inch. A yttrium-iron-garnet spherized ferrite element was mounted in the center of the hole and midway between the coil halves, and a permanent magnet was used which supplied a field of 800 oersteds. Direct current pulses having rise times of approximately one nanosecond seconds) with maximum amplitudes of 1000 amperes and greater and of approximately three nanoseconds duration were conducted through the coil, resulting in waveguide microwaves having energies of 320 watt nanoseconds. The microwaves consisted of monochromatic pulse trains and, by suitable adjustments of the tuning screws and shorting elements, their frequencies could be varied between 7 and 10 gHz. (10 cycles per second). The output power levels realized in the foregoing arrangement are several orders of magnitude higher than had been previously reported for arrangements using ferrite samples.

While an embodiment of the invention has been described and shown wherein the ferrite sample, slot resonator and pulsed fiield coil assembly of this invention are placed in a housing and associated with a waveguide, this should be considered as illustrative and not as a limitation upon the invention. Those skilled in the art can, for example, provide microwave strip line components in place of the waveguides and housing whereby the size of the structure may be considerably reduced.

There has accordingly been described and shown herein a ferrite device which does not suffer from the inherent power limitation of the earlier devices referred to above. A novel monolithic microcircuit element combining a pulsed magnetic field coil and a microwave resonator in a single unit has been demonstrated, which allows the high power capability of this type of device to be realized in practice in a device of very small size. This latter circuit element has the basic function of providing strong and efficient coupling between a ferrite and a microwave circuit in a microcircuit format, and is expected to have application to other microwave ferrite devices as well.

What is claimed is:

1. In a microwave generator of the type in which a coil is excited to provide a magnetic field for causing a ferrite body disposed centrally therein to oscillate, an improved structure for said coil comprising a substantially elongated rectangular block of conductive material having an opening extending along an axis through said block near one end thereof, a first slot extending through said one end of said block in a plane substantially perpendicular to the axis of said opening, and to a depth terminating beyond said opening, and a second slot extend ing from the other end of said block to said opening in a plane substantially perpendicular to the plane of said first slot.

2. In a microwave generator as recited in claim 1 wherein there is included a ferrite body disposed substantially centrally within the opening in said rectangular body, means for applying current pulses to the other end of said block for establishing a pulsed magnetic field passing in a first direction through said ferrite body, and means for establishing a steady state magnetic field passing through said ferrite body in a direction orthogonal to that of said pulsed magnetic field whereby microwaves are generated.

3. In a microwave generator as recited in claim 2 wherein there is included a waveguide structure, and means for coupling said generated microwaves to said waveguide structure comprising a conductive structure having a C shaped cross-section, said substantially rectangular block of conductive material being positioned with its one end and opening being substantially within the center of said C shaped cross-section of said means for coupling and having its other end in contact with and extending outward from between the ends of said C, and means for varying the frequency of the microwaves which are generated mounted in said conductive structure opposite said one end of said substantially rectangular block.

4. In a microwave generator as recited in claim 3 wherein said means for varying the frequency of the microwaves which are generated is a rutile disc, and screw means for supporting said disc threadably mounted in said conductive structure.

5. In a microwave generator which includes a waveguide structure and a ferrite element disposed within said waveguide structure, the improvement comprising a first coil means, a second coil means positioned coaxially with respect to said first coil means and spaced longitudinally therefrom a predetermined distance, to form a slot resonator therebetween, and means for supporting both said coil means within said waveguide structure with the coaxial axis of said first and second coil means positioned substantially in line with the length of said waveguide structure and with said slot resonator positioned transverse to the length of said waveguide.

6. The improvement in a microwave generator as defined in claim 5 wherein each of said first and second coil means is a single turn construction and there is a means for connecting said first and second coil means in parallel.

7. In a microwave generator as recited in claim 5 wherein said first and second coil means comprises an elongated substantially rectangular block of conductive material having an opening extending along an axis through said block near one end thereof, a first slot extending through said one end of said block in a plane substantially perpendicular to the axis of said opening to a depth terminating beyond said opening, and a second slot extending from the other end of said block to said opening in a plane substantially perpendicular to the plane of said first slot.

8. A microwave generator comprising a housing for attachment to a waveguide, said housing having a longitudinal axis and a waveguide aperture, a magnet for establishing a magnetic field in said Waveguide aperture, split coil means disposed within said Waveguide aperture tor defining a resonator slot oriented substantially transverse to said waveguide longitudinal axis, said split coil means having an axis extending in the direction of said waveguide longitudinal axis, conductor means attached to said split coil means for conducting current to said coil means, and ferrite means disposed in said resonator slot.

9. A microwave generator as defined in claim 8 wherein 6 said split coil means comprises two single turn coil sections electrically connected in parallel, said single turn coil sections being spaced a predetermined distance apart to form said resonator slot therebetween.

10. A microwave generator as defined in claim 8 including capacitor means mounted on said housing for movement toward and away from said resonator slot whereby to alter the fringe capacitance at an end of said slot to vary the resonant frequency of said slot resonator.

11. A microwave generator as defined in claim 8 wherein said housing is constructed of electrically conductive material, and extends less than 260 about said waveguide aperture, to form a slot, said conductor means projects through said slot of said housing and said split coil means are in contact with opposite walls of said slot, and including insulator means disposed in facewise engagement with said housing to conductively insulate it from the rest of said waveguide, whereby the path of current extends from said conductor means to said coil means and to the high inductance outer path formed by said housing.

No references cited.

JOHN KOMINSKI, Primary Examiner. 

1. IN A MICROWAVE GENERATOR OF THE TYPE IN WHICH A COIL IS EXCITED TO PROVIDE A MAGNETIC FIELD FOR CAUSING A FERRITE BODY DISPOSED CENTRALLY THEREIN TO OSCILLATE, AN IMPROVED STRUCTURE FOR SAID COIL COMPRISING A SUBSTANTIALLY ELONGATED RECTANGULAR BLOCK OF CONDUCTIVE MATERIAL HAVING AN OPENING EXTENDING ALONG AN AXIS THROUGH SAID BLOCK NEAR ONE END THEREOF, A FIRST SLOT EXTENDING THROUGH SAID ONE END OF SAID BLOCK IN A PLANE SUBSTANTIALLY PERPENDICULAR TO THE AXIS OF SAID OPENING, AND TO A DEPTH TERMINATING BEYOND SAID OPENING, AND A SECOND SLOT EXTENDING FROM THE OTHER END OF SAID BLOCK TO SAID OPENING IN A PLANE SUBSTANTIALLY PERPENDICULAR TO THE PLANE OF SAID FIRST SLOT. 